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Editorial - Biology & Medicine Case Reports (2018) Volume 2, Issue 2

The nitric oxide: A molecule of possible therapeutic use against aquatic stress in fishes.

Singh A*
Department of Zoology, R.K. Talreja College of Arts, Science and Commerce, University of Mumbai, Maharashtra, India

*Corresponding Author:

Singh A
Department of Zoology, R.K. Talreja College of Arts, Science and Commerce, University of Mumbai, Maharashtra, IndiaTel: 0251 273 0297E-mail:[email protected]

Abstract

In several toxicological research studies involving fish as animal model, it has been seen that fish die primarily because of suffocation caused due to dismantling of the vascular components followed by wear and tear and sloughing of epithelium layer of the respiratory organs such as gills and accessory respiratory organs (ARO) especially the air-breathing organs (ABO) found in some air-breathing fish species like Clarias batrachus, Clarias gariepinus, Anabas sp. etc. The gills are main respiratory organs and are fully aquatic in respiratory function while the ABO, on the other hand, are said to be aerial in nature i.e., extract the oxygen from atmospheric air. The ABO is hence more important for air-breathing fishes as they enable them to survive even in a condition of stress produced by ambient water contaminants/pollutants.

Editorial

In several toxicological research studies involving fish as
animal model, it has been seen that fish die primarily because
of suffocation caused due to dismantling of the vascular
components followed by wear and tear and sloughing of
epithelium layer of the respiratory organs such as gills and
accessory respiratory organs (ARO) especially the air-breathing
organs (ABO) found in some air-breathing fish species like
Clarias batrachus, Clarias gariepinus, Anabas sp. etc. The gills
are main respiratory organs and are fully aquatic in respiratory
function while the ABO, on the other hand, are said to be aerial
in nature i.e., extract the oxygen from atmospheric air. The
ABO is hence more important for air-breathing fishes as they
enable them to survive even in a condition of stress produced
by ambient water contaminants/pollutants. The gills, apart from
the role in breathing, also assist the fish in osmoregulation, in
maintaining acid-base balance and in getting rid of nitrogenous
waste materials produced in various metabolic reactions.
Both gills and ABO, as they purely reside in suprabranchial
chamber of either lateral side of fish head and always remain
in direct touch with external milieu are more vulnerable and are
probably affected first when the fish is exposed to any stressors/
contaminants in aquatic bodies/reservoirs. The researchers
have found that the fish, very often, try to compensate adverse
water quality conditions by flowing more and more blood in
blood capillaries and subepithelial blood vessels of the gills
and ABO. Thus, the overall efforts made by the fish create an
extra pressure on these delicate organs which ultimately results
in histomorphological manifestations including wear and tear,
dismantling of ladder like vascular components and sloughing
of surface epithelium leading to haemorrhage and ultimately
death of the fish. From research studies, it is clear that the
responses of these two vital organs towards aquatic stressors/
contaminants are almost compensatory in nature and perhaps
in the direction to minimise and/or neutralise the effects caused
for at least temporarily. This also corroborates the common
origin and similar anatomical patterns of the gills and ABO as
evidenced in several researches.

The Nitric Oxide (NO) detection in animal tissues and
elucidation of some of its biological role, in past few years,
has opened a new rationale for the biologists to do researches
in the field of biological sciences and especially the animal
sciences. In several research studies on mammals and other
animals including the fishes, it has been confirmed that NO play
very important role in many physiological functions including
neurotransmission and vasodilation. NO is a short lived gaseous
molecule and originates endogenously from oxidation of
L-arginine to L-citruline in response to receptor stimulation and
under catalytic control of Nitric Oxide Synthase (NOS) enzyme.
There are three isomers of NOS namely neuronal NOS (nNOS),
endothelial NOS (eNOS) and inducible NOS (iNOS) which
require nicotinamide adenine dinucleotide phosphate (NADPH)
as cofactor for generation of NO from L-arginine, a substrate
molecule for NO production in animal tissues/organs. In
cardiovascular system of the animals, during vasodilation, it is
established that NO is released as a part of adaptive mechanism
and enables blood vessels and hence the animal to respond
the changes in surrounding by regulating the blood flow and
maintaining the blood pressure through an action on the smooth
muscles of the vessels. In studies on some fishes, the presence of
NO synthesizing enzyme (NOS) in the gills has been evidenced.
The role of NO as vasodilator and more specifically, if I am
stating, stress (aquatic) reliever in fishes is however a matter of
great investigation. To elaborate and know more about the role
of NOS and hence the NO in gills and ABO of the fish, the work
has been initiated at Postgraduate Department of Zoology, R.K.
Talreja College of Arts, Science and Commerce, Ulhasnagar-3,
Maharashtra, India in the form of a small Research Project
(Minor Research Project) sanctioned from University Grants
Commission, Govt. of India, New Delhi, India.

The findings of Research Project will not only help the
Ichthyologists to understand, how the life of fishes can be saved
for longer time in such an era of huge industrialization and
urbanization and other human activities which are all together
life threatening to the fishes but also the Toxicologists to trace
out the possible pathways involved in vasodilatation process
(Figure 1).

Figure 1: A schematic representation indicating how the fishes will neutralize/minimize the effects of pollution and survive for longer time when
supplemented with NO.